1. Field of the Invention
This invention relates, in general, to the field of semiconductor manufacture. In particular, it relates to a method and apparatus for polishing semiconductor wafers wherein the useful life of the chemical mechanical polishing tool is prolonged.
2. Description of Related Art
Fabrication of semiconductor integrated circuits (IC) is a complicated multi-step process creating microscopic structures with various electrical properties to form a connected set of devices. As the level of integration of IC""s increases, the devices become smaller and more densely packed, requiring more levels of photolithography and more processing steps. As more layers are built up on the silicon wafer, problems caused by surface non-planarity become increasingly severe and can impact yield and chip performance. During the fabrication process, it may become necessary to remove excess material in a process referred to as planarization.
A common technique used to planarize the surface of a silicon wafer is chemical mechanical polishing (CMP). CMP involves the use of a polishing pad affixed to a circular polishing platen and a holder to hold the wafer face down against the rotating pad. A slurry containing abrasive and chemical additives are dispensed onto the polishing pad. The wafer and the polishing pad rotate relative to each other. The rotating action along with the abrasive and chemical additives of the slurry results in a polishing action that removes material from the surface of the wafer. Protrusions on the surface erode more efficiently than recessed areas leading to a flattening or planarization of the wafer surface.
As the layers to be removed on the wafer include different types of metal alloys, new chemical slurries must be used which are increasingly corrosive. Typically, the polishing pad sits directly over the rotating polishing platen. The pad itself is chosen for its ability to act as a carrier of the slurry and to wipe away the grit and debris resulting from the polishing action. Thus, the polishing platen is continually exposed to the slurry which leads to eventual corrosion of the platen itself diminishing its useful life. Replacement of the platen is expensive and time consuming thereby increasing manufacturing costs.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method and apparatus for decreasing the frequency of platen replacement.
It is another object of the present invention to provide a method and apparatus for prolonging the useful service life of the platen.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a chemical mechanical planarization tool comprising a polishing platen; and a disk-like platen top removably mounted on a top surface of the platen. Preferably, the platen top may comprise a material substantially impervious to a slurry used when planarizing an object, an insulative material, and/or a conductive material. Most preferably, the platen top comprises aluminum alloy or glass. The planarization tool may further include endpoint sensors attached to the platen top.
In another aspect, the present invention is directed to a chemical mechanical polishing tool comprising a polishing table; and a replaceable top removably mounted over the polishing table comprising a material substantially impervious to polishing slurries.
In yet another aspect, the present invention is directed to a chemical mechanical polishing tool comprising a polishing table; and a replaceable top removably mounted over the polishing table comprising borosilicate glass.
In still yet another aspect, the present invention is directed to a chemical mechanical polishing tool comprising a polishing table; and a replaceable top removably mounted over the polishing table comprising aluminum alloy.
In a further aspect, the present invention is directed to a method of prolonging the service life of a chemical mechanical planarization tool comprising the steps of: (a) providing a chemical mechanical planarization tool having a rotatable polishing platen; (b) removing a portion of a top surface of the platen; (c) providing a removable platen top having a substantially similar size and shape of the platen, the platen top comprising a material adapted to withstand a slurry used during activation of the planarization tool; and (d) attaching the platen top to the platen to substantially protect the platen from erosion caused by the slurry.
In a final aspect, the present invention is directed to a method of polishing semiconductor wafers comprising the steps of providing a chemical mechanical polishing tool comprising a rotatable platen; a replaceable platen top disposed over the platen; and a polishing pad disposed over the platen, wherein the platen top substantially protects the platen from erosion; providing at least one semiconductor wafer in need of polishing; and chemical mechanical polishing the wafer with a slurry provided to the polishing pad, the slurry capable of eroding the tool over time.